For low energies, which effect is the most common process of absorption?

• A. Compton effect
• B. Photoelectric effect
• C. Rayleigh scattering
• D. Pair production

Answer: (B)

In the context of low-energy photons, the photoelectric effect is indeed the most common process of absorption. This phenomenon occurs when a photon interacts with an electron in an atom, transferring all of its energy to the electron, which is then ejected from the atom. This interaction is more likely to occur with low-energy x-rays and gamma rays because their energy levels are typically lower than the binding energy of inner shell electrons in materials, such as bone or soft tissue.

The probability of the photoelectric effect occurring increases significantly as the energy of the photon decreases and as the atomic number (Z) of the absorbing material increases. In bone densitometry, where the primary goal is to evaluate the calcium content in the bone, this effect is especially important because it contributes to the attenuation of x-rays, allowing for effective measurement of bone mineral density.

In contrast, while other processes like the Compton effect, Rayleigh scattering, and pair production can occur, they are not as relevant in the context of low-energy photon interactions. The Compton effect is associated with higher energy photons where scattering and partial energy loss occur, making it less significant for the low-energy range of interest. Rayleigh scattering involves elastic scattering without energy loss, and pair production only becomes significant